venerdì 18 marzo 2016

STATO DELL'ARTE. studies of many different traits tend to find that ~50% of the variation is heritable and ~50% is due to non-shared environment, with the contribution of shared environment usually lower and often negligible. This is typically summarized as “50% nature, 50% nurture”. That summary is wrong.

DISCARICA.Non-shared environment isn’t really “non-shared environment” the way you would think. It’s more of a dumpster. Anything that isn’t genetic or family-related gets tossed into the non-shared environment term. Here are some of the things that go into that 50% non-shared environment:

ERRORI. Measurement error is neither genetics nor family, so it ends up in the non-shared environmental term. ..

Imagine a world where intelligence is entirely genetic. Some identical twins take an IQ test, one makes some lucky guesses, the other is tired, and they end up with a score difference of 5 points. Then some random unrelated people take the test and they get the 5 point difference plus an extra 20 point difference from genuinely having different IQs. In this world, scientists would conclude that about 80% of IQ is genetic and 20% is environmental. But in fact in terms of real, stable IQ differences, 100% would be genetic and 0% environmental....

Riemann and Kandler (h/t JayMan) run a study which is an excellent demonstration of this. Classical twin studies sometimes use self-report to determine personality – ie they ask people to rate how extraverted/conscientious/whatever they are. These studies find that most personality traits are about 40% genetic, 60% non-shared environmental. Riemann and Kandler obsessively collect every possible measurement of personality – self-report, other-report, multiple different tests – and average them out to get an unusually accurate and low-noise estimate of the personality of the twins in their study. They find that variation in personality is about 85% genetic, 15% non-shared environmental. So it looks like much of the non-shared environmental variation in traditional studies of personality was just error.

FORTUNA TRADIZIONALE. Bob becomes a junior advertising executive at Coca-Cola, where he designs a new ad targeting young female consumers. His identical twin Rob becomes a junior advertising executive at Pepsi-Cola, where he designs his own new ad targeting young female consumers. Both ads are very successful – in fact, exactly equally successful. But Coke’s CEO is a crony capitalist who wants to replace everyone in the company with his college buddies, so he ignores Bob’s good work and demotes him to a low-level position.

FORTUNA BIOLOGICA. The genome can’t encode the location of every cell in the body. Instead, it specifies high-level processes which create lower-level processes which create those cells. .. Thus, identical twins have different fingerprints, different freckles, and different birthmarks... The immune system. Immunology is still poorly understood, but it seems very important. Immune reactions and neuroinflammation have been implicatedto one degree or another in a lot of psychiatric diseases.

EPIGENETICA. We know that identical twins have substantially differentepigenetics, and there are hints that this underlies discordant behavior.

One of these – or maybe some 3e I don’t know about – is probably the reason for less-than-perfect twin concordance in conditions like Parkinson’s disease, migraine, autism, and schizophrenia. Needless to say, anything that can make you schizophrenic can probably affect your personality and life outcomes pretty intensely.... But all of this gets counted as “non-shared environment” in a twin study, and used to play up the importance of schools and peer groups.

TURKHEIMER. ... concludes: “We emphasize that these findings should not lead the reader to conclude that the nonshared environment is not as important as had been thought.” But although I have a huge amount of respect for Turkheimer, I kind of want to conclude that the nonshared environment is not as important as had been thought. My guess is that the nonshared environment as Turkheimer discusses it – differential parenting, schools, peers, and so on – is only a fraction of the “nonshared environmental” term in genetics studies.

If that were true, it would mean that nature is more important than we thought relative to environment in terms of things we can understand and possibly affect. That would make the quest to change important outcomes like intelligence, personality, income, or criminality by changing society even more daunting. And it would make the opportunity to change those outcomes through genetic engineering even more tempting.

Non esiste il gene del... Esempio: il crimine. Crime is heritable. And yet, there is no crime gene. The fact that we have to write such a qualification speaks to a woeful ignorance of genetics that pervades much of the public and academia. Mercifully, we can sidestep long discussions of molecular biology and skip right to the “law” that takes the possibility of a crime gene off the table. It is in fact, the newly dubbed “4th Law of Behavior Genetics” and it’s quite simple. For complex traits, there are, for the most part, likely hundreds or thousands of genes involved, most of which generally contribute only very small effects to any given outcome. Not only are there many genes involved, but the complexity of how these genes operate is amazing. There are genes that influence other genes, genes that assemble neurons and run them, and genes that perform any number of other banal processes in the body.

Interazione geni ambiente sopravvalutata. An eager public and a misinformed segment of the academy has caricatured the science and turned these two topics into nonsense. As Pinker notes, “it’s all about interactions” and other such rallying cries are used reflexively rebut discussions like this one. Do not fall into that trap. As we’ve said countless times, both genes and the environment matter, but that does not mean that they always interact in a statistical sense, and itdoesn’t meanthat “everything” is an “interaction.” Writers(including the authors of this essay) continue to make this point, and yet it continues to be ignored. While there are some social scientists that argue that genetic effects can only surface when triggered by environmental stimuli, they are flat-out wrong. Yes, there is evidence indicating that genetic effects can be dependent on environmental exposure, but there is also evidence that genes can have effects on behavioral phenotypes that are fullyindependent of gene-environment interactions.